1. Field of the Invention
The invention relates to a wakefulness level estimation apparatus that estimates a level of wakefulness of a person (subject person).
2. Description of the Related Art
Various types of apparatuses that estimate a state of wakefulness of a driver (subject person) have been proposed for the use in a driver assist system, etc. For example, Japanese Patent Application Publication No. 2006-109980 (JP-A-2006-109980) describes an apparatus that detects the degree of opening of an eye of a driver (hereinafter referred to as “eye-opening degree”), and determines a level of wakefulness of the driver based on a difference between the detected eye-opening degree and a reference value of the eye-opening degree. The reference value of the eye-opening degree is set based on data on the eye-opening degree (hereinafter referred to as “eye-opening degree data”) taken when it is determined that the driver is awake, such as when the driver speaks or the driver consciously operates a vehicle.
However, even when the driver speaks or consciously operates the vehicle, it is still likely that the driver's level of wakefulness is low. If the reference value of the eye-opening degree is set based on the eye-opening degree data taken under such circumstances, the set reference value is not proper one, and therefore, it is not possible to estimate the level of wakefulness with high accuracy. Further, when the reference value of the wakefulness level correlation value and the wakefulness level estimation function, etc. are set by a statistical method, the results of estimation of the level of wakefulness vary among different individuals. Further, even when only one person is subjected to the estimation of the level of wakefulness, the estimation results intra-individually vary depending on, for example, personal conditions on the day of estimation. Further, if an actuation to awaken the driver (hereinafter referred to as “awakening actuation”) is performed based on the estimation results thus obtained, timing at which the awakening actuation is performed may be delayed, or the awakening actuation may be unnecessarily performed.